Gather your materials:

With the colored marker, color one of the styrofoam cups and set it aside so you can use it as your starting point when measuring the wind speed.

Take one cup for your center piece and poke the straws through making a cross "+" shape in the center and tape the cross section together to hold. Now take one of the pencils and poke it through the bottom of the cup so that the eraser end is up under the cross section of the straws. Place the straight pin through the straw center into the eraser to hold. Don't make the pin too tight as this is the axis on which your anemometer will turn.

Take the remaining 3 cups and the colored cup and poke the other ends of the straws through the sides of the cups. Make sure they are all facing the same direction. Now place your anemometer in the ground with the pencil end.

When the wind blows, start counting how many times the colored cup goes by in one minute. That's the speed of the wind. For example, if the cup makes 10 complete revolutions in one minute, the wind speed is 10mph.